Start by trimming any large pieces of fat from your boneless chuck roast. Season the meat generously with kosher salt and freshly ground black pepper on all sides.
In a skillet over medium-high heat, add the olive oil. Once hot, sear the roast on all sides until it’s beautifully browned (about 4-5 minutes per side).
Place the seared roast in your slow cooker. Sprinkle the onion soup mix and Ranch seasoning mix evenly over the top. Pour the pepperoncini pepper juice around the roast and add the whole or sliced pepperoncini peppers. Finally, scatter the cubed butter on top.
Cover the slow cooker and cook on low for 8-10 hours, or on high for 4-6 hours. The longer, the better!
Once cooked, shred the meat using two forks, right in the slow cooker. Stir the meat into the juices for maximum flavor. Garnish with freshly minced parsley if desired, and serve hot.